Full-dimension MIMO (FD-MIMO) is a key technology introduced in 3GPP wireless communication systems to significantly increase system capacity. In FD-MIMO networks, an eNB deploys a large number of active antenna elements on a two-dimensional plane, i.e., a 2-dimensional (2D) active antenna array (AAA). With such antennas, an eNB can form beams steered towards angles on both horizontal and vertical directions, and is capable of supporting high-order MU-MIMO while fully exploiting spatial degrees of freedom. To realize the FD-MIMO gain, an eNB may acquire channel state information (CSI) of user equipments (UEs). For frequency division duplexing (FDD) systems, a CSI is acquired by training (e.g. via CSI reference signal (CSI-RS)) and feedback of precoding matrix indicator (PMI).